1. Field of the Invention
The present invention relates to an optical path switching device and relates for example to an optical path converter suitable for application to an optical cross connector device or an optical add/drop multiplexer or optical switch device.
2. Description of Related Art
In recent years, in optical network systems suitable for high transmission rates and increased capacity, close attention is being paid to optical signal multiplexing techniques.
A time division multiplexing (TDM) system is a system whereby a plurality of signals can be time-wise multiplexed and transmitted by a single transmission path. In this system, when the capacity per channel or the number of channels is increased, high-speed optical transmitters/receivers and electrical circuitry are required. Recently, also, optical time division multiplexing (OTDM) systems using optical pulses (RZ signals) have been studied; however, with such OTDM systems, the same level (rate) of electrical processing is involved as in the case of TDM systems. Wavelength division multiplexing (WDM) is a system in which multiplexing is performed using wavelength; with this WDM system, transmission capacity can be increased without raising the signaling rate. However, with the WDM system, in order to ensure a large number of channels (number of wavelengths), it is necessary to take measures in regard to wavelength stabilization of the signal transmission/reception unit (light source/optical filter), which increase costs. Equipment that is currently practically used provides a number of channels of about 100 wavelengths, but is expensive. These techniques are effective for transmitting enormous quantities of data such as for a backbone system.
A different technique from the techniques described above for increasing the degree of multiplexing which is being studied is the optical code division multiple access (OCDM) technique. Although the optical code division multiple access system is in itself inferior to other multiplexing techniques, it can easily be combined with other techniques, so where, for example in a wavelength division multiplexing system, it is difficult to increase the number of wavelengths, an increase in the number of channels can be achieved by combining the wavelength multiplexing technique and the optical code division technique.
Also, in the case of backbone networks, use of optical cross connector devices (OXC) or optical add/drop multiplexers (OADM) is being studied. In such devices, the communication path is changed with the signal still in the form of light, without converting it to an electrical signal. Such optical path alterations were conventionally performed using an optical switch.
The changeover speed of currently used optical switches is a few “ms”, so it is difficult to achieve much increase in speed of optical path changeover without devising a new optical path changeover system. In other words, with an OXC or OADM using an optical switch, only restoration changeover (said to require about 50 ms in the case of SDH) can be performed and changeover without any momentary interruption (changeover time 1 ms or less) or dynamic changeover in response to traffic is difficult to achieve.